Vertical LED chip package on TSV carrier

ABSTRACT

A method of forming a light-emitting device (LED) package component includes providing a substrate; forming an LED on the substrate; and lifting the LED off the substrate. A carrier wafer is provided, which includes a through-substrate via (TSV) configured to electrically connecting features on opposite sides of the carrier wafer. The LED is bonded onto the carrier wafer, with the LED electrically connected to the TSV.

TECHNICAL FIELD

This disclosure relates generally to light-emitting device (LED) packagecomponents, and more particularly to vertical LED packages includingthrough-substrate vias (TSVs).

BACKGROUND

In recent years, optical devices, such as light emitting diodes (LEDs),laser diodes, and UV photo-detectors have increasingly been used.Group-III nitride compounds, such as gallium nitride (GaN) and itsrelated alloys have been known suitable for the formation of the opticaldevices. The large bandgap and high electron saturation velocity of thegroup-III nitride compounds also make them excellent candidates forapplications in high-temperature and high-speed power electronics.

Due to the high equilibrium pressure of nitrogen at typical growthtemperatures, it is extremely difficult to obtain GaN bulk crystals.Therefore, GaN layers and the respective LEDs are often formed on othersubstrates that match the characteristics of GaN. Sapphire (Al₂O₃) is acommonly used substrate material. FIG. 1 illustrates a cross-sectionalview of a package component including LED 2. LED 2, which includes aplurality of GaN-based layers, is formed on sapphire substrate 4.Sapphire substrate 4 is further mounted on lead frame 6. LED 2 furtherincludes electrodes 8 and 10 electrically connected to lead frame 6through gold wires 12.

Because sapphire has a low thermal conductivity, heat generated by LED 2cannot be dissipated through sapphire substrate 4 efficiently. The heatneeds to be dissipated through the top end of LED 2, and through goldwires 12. However, since gold wires 12 are relatively long since theyhave to extend to lead frame 6, the thermal conductivity through goldwires 12 is also low. In addition, electrodes 8 and 10 occupy chip area,and hence the LED light output area is not optimized.

SUMMARY

In accordance with one aspect, a method of forming a light-emittingdevice (LED) package component is provided, including forming an LED ona substrate; and lifting the LED off the substrate. A carrier wafer isprovided that includes a through-substrate via (TSV) configured toelectrically connect features on opposite sides of the carrier wafer.The LED is bonded onto the carrier wafer, with the LED electricallyconnected to the TSV.

Other embodiments are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates a cross-sectional view of a conventionallight-emitting device (LED) package structure formed on a sapphiresubstrate; and

FIGS. 2 through 7 are cross-sectional views of intermediate stages inthe manufacturing of a package component including at least one LED chipin accordance with various embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative and do not limit the scope of the disclosure.

A novel light-emitting device (LED) package component and the method offorming the same are presented. The intermediate stages of manufacturingan embodiment are illustrated. The variations of the embodiment are thendiscussed. Throughout the various views and illustrative embodiments,like reference numbers are used to designate like elements.

FIG. 2 illustrates wafer 100, which includes LED 22 formed on substrate20. In an embodiment, substrate 20 is formed of sapphire (Al₂O₃),although it may also be formed of other materials having characteristicsclose to the characteristics of the LED formed thereon (which maycomprise group-III and group-V elements, or also known as III-V compoundsemiconductor materials).

Un-doped gallium nitride (u-GaN) layer 24 or another heat sensitivematerial is formed above, and possibly contacts, substrate 20. In anembodiment, u-GaN layer 24 is substantially free from elements otherthan Ga and N. LED 22 is formed on top of, and may possibly contact,u-GaN layer 24. LED 22 may include a plurality of layers. Accordingly tovarious embodiments, LED 22 includes at least one multiple quantum well(MQW), a first group-III nitride (III-nitride) layer doped with a firstimpurity of a first conductivity type under the MQW, and a secondIII-nitride layer doped with a second impurity of a second conductivitytype opposite the first conductivity type over the MQW. The group-IIInitride layers are each connected to a TSV in the carrier wafer.

In an exemplary embodiment, LED 22 includes n-GaN layer (GaN doped withan n-type impurity) 26, multiple quantum well (MQW) 28, p-GaN layer (GaNdoped with a p-type impurity) 30, reflector 32, and top electrode 34.Reflector 32 may be formed of an indium tin oxide (ITO), for example.MQW 28 may be formed of, for example, InGaN, and acts as an active layerfor emitting light. The formations of layers 26, 28, 30, 32, and 34 areknown in the art, and hence are not disclosed in detail herein. In anexemplary embodiment, the formation methods of layers 26, 28, 30, and 32may include epitaxial growth. It is realized that LED 22 may have manydesigns, and FIG. 2 only shows an exemplary version among the availablevariations. For example, the materials of each of the layers 26, 28, 30,and 32 may be different from the above-discussed material, and may beternary III-V compound semiconductor materials. Also, the positions ofn-GaN layer 26 and p-GaN layer 30 may be swapped.

LED 22 as shown in FIG. 2 may represent a plurality of LEDs, eachcomprising one electrode 34, although only one LED 22 is illustrated.Referring to FIG. 3, LED(s) 22 are lifted off substrate 20. In anexemplary embodiment, substrate 20 is exposed to light energy, forexample, a laser beam (symbolized by arrows), projecting from the bottomof substrate 20. The laser beam penetrates through substrate 20 to layer24. As a result, layer 24 is decomposed by the heat resulting from thelaser beam, and hence LED(s) 22 are separated from substrate 20. In anembodiment, the laser is a KrF laser with a wavelength of about 248 nm.After the lift-off, LEDs 22 are separated from each other, with each ofLEDs 22 including one electrode 34.

Referring to FIG. 4A, carrier wafer 40 is provided. Carrier wafer 40 maycomprise substrate 48, which may be a semiconductor substrate, such as asilicon substrate, or may be a dielectric substrate. Through-substratevias (TSVs) 42 (denoted as 42A and 42B) are formed in substrate 48 andelectrically connect features on opposite sides of carrier wafer 40.TSVs 42 may comprise copper or other metals, such as tungsten, or alloysthereof. Solder balls 46 may be mounted on one side of substrate 48 andon TSVs 42. On each side of carrier wafer 40, filled TSVs 42 mayprotrude out of the surface slightly. Alternatively, bond pads (such asbond pads 44) may be formed on filled TSVs 42.

In various embodiments, carrier wafer 40 includes active circuitstherein, as is schematically illustrated in FIG. 4B. In theseembodiments, carrier wafer 40 may comprise a semiconductor substrate,such as a silicon substrate (denoted as 48′). Accordingly, TSVs 42 maybe through-silicon vias. An exemplary active circuit (symbolized by anMOS device) 50 is schematically shown as being formed at the surface ofsemiconductor substrate 48′. Active circuit 50 may include CMOS devices(PMOS devices and NMOS devices), capacitors, diodes, or the like. Activecircuit 50 may also include desirable CMOS circuits such aselectro-static discharge (ESD) circuits/devices, which may be used toprotect the optical devices mounted thereon, and/or driver circuits, forexample, for driving the LEDs bonded on carrier wafer 40. Inter-metaldielectric (IMD) layers 52 may be formed over active circuit 50. Metallines and vias (not shown) may be formed in IMD layers 52 tointerconnect the devices in active circuit 50. In alternativeembodiments, no active circuit is formed in carrier wafer 40.

Referring to FIG. 5, a plurality of LEDs 22 is bonded onto carrier wafer40. The adhesion of LEDs 22 to carrier wafer 40 may be achieved throughconductive thermal interface material (TIM) layer 56. In an embodiment,each of conductive TIM layers 56 has a similar size as that of LED 22.In alternative embodiments, conductive TIM layer 56 includes a pluralityof discrete components, each corresponding to one of TSVs 42B and/or thebond pad formed thereon. Conductive TIM layers 56 may be formed ofsolder, metals, conductive organic materials, or the like, providing thematerials have electrical and thermal conductivities suitable for LEDoperation. The bonding between LEDs 22 onto carrier wafer 40 may beperformed through the reflow of the solder or through directmetal-to-metal bonding, depending on the materials of conductive TIMlayers 56.

With LEDs 22 being bonded onto carrier wafer 40, n-GaN layers 26 in LEDs22 are electrically connected to TSVs 42B and solder balls 46 throughrespective conductive TIM layers 56. Accordingly, solder balls 46 may beused to conduct a voltage to LEDs 22. Further, the heat generated in LED22 may be conducted to carrier wafer 40 through the respectiveconductive TIM layers 56.

FIG. 6 illustrates the wire-bonding of electrodes 34 to bond pads 44,wherein conductive wires 58 are used to electrically connect electrodes34 to TSVs 42A. Conductive wires 58 may be gold wires or copper wiresalthough they may also be formed of other metallic materials. Referringto FIG. 7, silicone lenses 60 are molded onto LEDs 22. The molding ofsilicone lenses 60 is known in the art, and hence is not disclosed indetail herein. Each of silicone lenses 60 may cover the respective LEDs22 and wires 58.

Carrier wafer 40 may then be diced or sawed along scribe lines 62, sothat LED package components are separated individually. Blades or lasermay be used to dice or saw the carrier wafer. Accordingly, carrier wafer40 is separated into a plurality of carrier chips, with each beingbonded to one of LEDs 22. It is noted that in the above-discussedembodiments, the bonding of LEDs 22 and the wire bonding are performedat wafer level before carrier wafer 40 is diced or sawed. In alternativeembodiments, the bonding of LEDs 22 and the wire bonding are performedat chip level after carrier wafer 40 is diced. In these alternativeembodiments, one LED 22 is bonded onto a carrier chip that has alreadybeen sawed from carrier wafer 40.

As shown in FIG. 7, the electrical connection to the bottom of LED 22 ismade through TSVs 42B. Accordingly, the LED light output area isincreased since the connection to n-GaN layer 26 no longer requiresadditional chip area. Further, carrier wafer 40 has significantly higherthermal conductivity than a sapphire substrate, partially due to theconductive TIM layers 56, silicon (in substrate 48), and the pluralityof TSVs 42B (which may be formed of copper) all having higher thermalconductivities than sapphire. The thermal conductivity of carrier wafer40 may be ten times higher than that of a sapphire substrate or evenhigher. The electrical conductivity to LED 22 may also be improved byusing a plurality of TSVs 42B.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A method of forming a light-emitting device (LED)package component, the method comprising: providing a substrate;epi-growing an LED on the substrate, wherein the epi-growing the LED onthe substrate is performed so that a first side of the LED faces thesubstrate; lifting the LED off the substrate; providing a carrier wafercomprising a first through-substrate via (TSV) configured toelectrically connect features on opposite sides of the carrier wafer;and bonding, after the LED has been lifted off the substrate, the LEDonto the carrier wafer, with the LED electrically connected to the firstTSV, wherein the bonding the LED onto the carrier wafer is performed sothat the LED is bonded to the carrier wafer through the first side ofthe LED.
 2. The method of claim 1, wherein the step of lifting the LEDoff the substrate comprises using a laser beam to decompose anintermediate layer between the substrate and the LED.
 3. The method ofclaim 2, wherein the intermediate layer comprises undoped GaN.
 4. Themethod of claim 3, wherein the substrate is a sapphire substrate, andwherein the epi-growing the LED comprises: epi-growing the intermediatelayer on the sapphire substrate, the intermediate layer being inphysical contact with the sapphire substrate; and epi-growing the LED onthe undoped gallium nitride layer, the LED being in physical contactwith the intermediate layer.
 5. The method of claim 1, wherein the LEDcomprises: a multiple quantum well (MQW); a first group-III nitride(III-nitride) layer doped with a first impurity of a first conductivitytype under the MQW, wherein the first TSV is electrically connected tothe first III-nitride layer; and a second III-nitride layer doped with asecond impurity of a second conductivity type opposite the firstconductivity type over the MQW.
 6. The method of claim 5, wherein thefirst conductivity type is n-type, and the second conductivity type isp-type.
 7. The method of claim 5 further comprising performing a wirebonding to electrically connect the second III-nitride layer to a secondTSV in the carrier wafer.
 8. The method of claim 1 further comprisingdicing the carrier wafer.
 9. The method of claim 1, where in the step ofbonding the LED onto the carrier wafer comprises applying a thermalinterface material between the LED and the carrier wafer.
 10. A methodof forming a light-emitting device (LED) package component, the methodcomprising: providing a sapphire substrate; epi-growing a plurality ofLEDs on the sapphire substrate, each LED containing a light-emittinglayer, a first doped layer having a first type of conductivity, and asecond doped layer having a second type of conductivity different fromthe first type of conductivity, wherein the forming the plurality ofLEDs is performed such that the first doped layer is located closer tothe sapphire substrate than the second doped layer; projecting a laseron the sapphire substrate to separate the plurality of LEDs from thesapphire substrate; bonding, after the plurality of LEDs have beenseparated from the sapphire substrate, the plurality of LEDs onto afirst plurality of through-substrate vias (TSVs) in a carrier wafer,wherein the bonding the plurality of LEDs is performed such that thefirst doped layer is located closer to the carrier wafer than the seconddoped layer after the bonding; and performing a wire bonding to connecta top electrode in each of the plurality of LEDs to one of a secondplurality of TSVs in the carrier wafer.
 11. The method of claim 10,wherein the step of bonding the plurality of LEDs onto the firstplurality of TSVs comprises bonding a conductive thermal interfacematerial between, and contacting, a III-nitride layer and at least oneof the first plurality of TSVs.
 12. The method of claim 10, wherein eachof the plurality of LEDs is bonded to more than one of the firstplurality of TSVs without using bond wires.
 13. The method of claim 10further comprising molding a plurality of silicon lens on each of theplurality of LEDs.
 14. The method of claim 1, wherein the carrier wafercontains an active circuit.
 15. The method of claim 10, wherein thecarrier wafer contains an active circuit and an inter-metal dielectric(IMD) layer.
 16. A method, comprising: growing a light-emitting diode(LED) on a first substrate through an epitaxial growth process; removingthe first substrate from the LED; and thereafter bonding the LED to asecond substrate, the second substrate containing a via that extendthrough the second substrate; wherein the bonding is performed suchthat: the LED is electrically coupled to the via; and a side of the LEDfrom which the first substrate is removed is bonded to the secondsubstrate.
 17. The method of claim 16, further comprising: forming anelectrode contact on the LED; and wherein: the LED contains a firstlayer with a first type conductivity and a second layer with a secondtype conductivity opposite the first type; the forming the electrodecontact is performed such that the electrode contact is electricallycoupled to the first layer of the LED; and the bonding the LED isperformed such that the via is electrically coupled to the second layerof the LED.
 18. The method of claim 16, wherein the second substratecontains one or more active circuits and an inter-metal dielectric (IMD)layer.
 19. The method of claim 5, wherein the bonding is performed suchthat the first TSV is electrically coupled to the first III-nitridelayer without bond wires.
 20. The method of claim 17, wherein: theelectrode contact is electrically coupled to the first layer of the LEDthrough a bond wire; and the via is electrically coupled to the secondlayer of the LED without any bond wires.